"Cryotherapy" is defined as the treatment of injury using the benefits derived by application of both cold and pressure. Such therapy has been shown to be particularly effective in treating musculoskeletal trauma resulting from a severe blow or by the application of a wrenching force to the body, e.g. lacerations, sprains, strains and fractures. This type of injury may be accompanied by a tearing of tendons, ligaments or other tissue, and starts the body's own natural healing process. See Sloan et al., "Effects of Cold and Compression on Edema", The Physician and Sports Medicine, 16(8) (1988); Bailey, "Cryotherapy", Emergency, 40-43 (August, 1984); Cryomed Brochures.
In order to minimize secondary trauma subsequent to a primary musculoskeletal insult, prompt treatment is required. This treatment should immobilize the trauma site, ease pain and minimize the risk of secondary tissue damage which usually accompanies breaks, sprains and strains.
An injury will almost immediately produce pain and will be followed rapidly by an accumulation of blood, interstitial fluids and lymphatic fluids. In addition, injured cells will release histamine and other substances which act to perpetuate the inflammation process and increase the permeability of the vasculature. For a number of reasons, a free radical process ensues. The inflammatory process also causes the release of chemicals and causes conditions under which damaged collagen dissolves. The extent of this collagen damage depends on a number of factors, including the extent of the inflammatory process.
The collagen removal process forms a part of the normal healing process, and under certain circumstances, is desirable in that it allows reconstruction of the tissue by collagen regrowth. Unfortunately, in most circumstances, the damaged collagen is replaced by a random regrowth, forming a scar. While scar formation may be necessary to replace the lost tissue matrix, in many circumstances the scar impairs a return to normal functioning. Thus, scar formation in a joint, where uninjured collagen is linearly dispersed, tends to proceed after the injury by randomly-fashioned replacement, which may interfere with joint mobility and produce chronic pain.
The body's healing response is natural and necessary for restoring the functioning of the damaged tissue and the body as a whole. This natural process may produce detrimental side effects that, if not properly controlled, can exacerbate patient discomfort, impede recovery and result in long term or permanent impairment of the injured area.
Damage to the tissue may allow the formed blood components to leave the vasculature in the area of the injury (called a "hematoma"). Enhanced permeability of the blood vessels may lead to an accumulation of fluids in the extracellular space (called "edema"). This fluid causes swelling, which may form part of a self-perpetuating process of inflammation. Further, in circumstances when the pressure in the tissue exceeds the perfusion pressure in the capillary microcirculation, the flow of oxygenated blood in that tissue becomes insufficient and the tissue becomes hypoxic, eventually leading to hypoxic necrosis. This process, called a "compartment syndrome", may occur when an external pressure is applied to tissues which exceeds the perfusion pressure, or when an inflammatory process in the tissue causes the buildup of interstitial fluid with an increase in pressure.
Secondary trauma is a process by which a primary injury causes inflammation, edema and/or hematoma, which secondarily is responsible for further tissue damage. If the secondary process is treated, slowed or its course modified, the extent of this secondary injury may be reduced. Thus, after a musculoskeletal injury, edema and/or hematoma may result, causing tissue compression and other effects. This compression can result in further injury while the swelling lasts, and prevent other treatments from being effectively applied. Under normal circumstances, secondary trauma lasts approximately one to three days after a primary musculoskeletal insult, and during this period, further treatment, including surgery, may have to be postponed.
It is known that the immediate application of compression and cold will slow down tissue metabolism and response to injury so that a slower and more controlled process may ensue. Thus, the art teaches the use of ice pack compresses. Additionally, U.S. Pat. No. 3,871,381 to Roslonski teaches the introduction of a pressurized volatile refrigerant through a controlled flow rate valve, which cools a maze-passage in a flexible device. A pressure relief valve maintains a back-pressure in the system.
Besides injuries, there are other applications for cryotherapy. For example, normal tissues, such as hair follicles, may be spared the effects of cancer chemotherapy by the topical application of pressure and cold around the time of chemotherapeutic treatments. See, e.g., Dean, J. C. et al., "Prevention of Doxorubicin-induced Scalp Hair Loss," New England Journal of Medicine, Dec. 27, 1979, 301(26):1427-29; H. F. P. Hillen, et al., "Scalp cooling by cold air for the prevention of chemotherapy-induced alopecia," Netherlands Journal of Medicine, 37 (1990) 231-235; Cline, B. W., "Prevention of chemotherapy-induced alopecia: a review of the literature," Cancer Nursing, 1984, 7:221-228; Dean, J. C., et al. "Scalp hypothermia: A comparison of ice packs and the Kold Kap in the prevention of doxorubicin-induced alopecia," J. Clin. Oncol., 1983, 1:33-37; Bulow J., et al., "Frontal subcutaneous blood flow, and epi- and subcutaneous temperatures during scalp cooling in normal man," Scand. J. Clin. Lab Invest., 1985, 45:505-508; Parbhoo, SP, et al., "An improved technique of scalp hypothermia to prevent adriamycin/mitozantrone induced alopecia in patients with advanced breast cancer," Clinical Oncology and Cancer Nursing, Stockholm, 1985, 232 (abstract); Gregory, R. P., et al., "Prevention of doxorubicin-induced alopecia by scalp hypothermia: relation to degree of cooling," Br. Med. J., 1982, 284:1674. Chemotherapeutic agents which cause alopecia which may be reduced by cryotherapy include anthracycline antibiotics, e.g. doxorubicin or epirubiicin, nucleoside analogs, e.g. 5-fluorouracil, folate antagonists, e.g. methotrexate and alkylating agent, e.g. cyclophosphamide.
In addition, cryotherapy may also be employed for other medical purposes, where control of metabolic rate is desired.
For example, U.S. Pat. No. 3,821,381 to Roslonski relates to a system for applying pressure and cold to an injury, using chlorofluorocarbons as a refrigerant fluid. It is also known to circulate a cooled fluid through a conduit in a bandage. Cold and pressure are therefore known treatments for traumatic injuries, as well as inflammatory pathologic processes which involve externally accessible organs.
Additionally, the device disclosed in Roslonski, U.S. Pat. No. 3,871,381 relates to a system for applying cold and pressure to an injury using a fluorocarbon refrigerant. This system, however, presents a number of drawbacks. First, the design of Roslonski's flow path allows refrigerant liquid to pool in some areas, while other areas do not receive liquid, thus causing uneven tissue cooling. Further, a crimp in one portion of the device may block a flow of coolant liquid to other portions of the device, likewise causing uneven cooling and additionally causing noise.
The temperature of these known systems depend in large part on the composition of the refrigerant fluid employed, which has a boiling plateau slightly above the freezing point of water. These systems therefore allow the maintenance of the device at a slightly higher temperature. These known systems also have an operating temperature which depends in lesser part on the rate at which heat is removed by the refrigerant, which in turn depends on the rate of volatization of the refrigerant. Other performance factors include the ambient temperature, body temperature, atmospheric pressure, pressure within the device, refrigerant composition and flow rate of the refrigerant.
Chlorofluorocarbon refrigerants are known to be available and to be used alone or in mixtures. Some mixtures have a boiling characteristic with a plurality of plateaus. Known refrigerants like Freon 11, Freon 12 and Freon 114 have boiling points of approximately 75 F. (24 C.), -22 F. (-30 C.) and 39 F. (3.8 C.) respectively, and these may be mixed to form a refrigerant solution having approximately the same boiling plateaus. See Freon Product Information, Du Pont (1973). In practice, the lowest boiling component of such a refrigerant mixture acts to propel the refrigerant from the canister and precool the remaining refrigerant liquid as it enters the maze. The mid temperature boiling refrigerant acts to cool the tissue by boiling in the maze at a temperature approximately the same as the desired tissue temperature. Lastly, the highest boiling component acts as a heat transfer agent to improve the effectiveness of the device, since it vaporizes before it reaches the bladder. Thus, the lowest temperature in the heat transfer portion of the cryotherapy device, using the known refrigerants, will be around 36-39 F., thereby posing a small risk of tissue freezing, unless too much refrigerant mixture is injected so that the lowest boiling component is present in substantial quantities. These mixtures, therefore, may be used in open-loop cryotherapy systems, with minimal or imprecise flow regulation, and with low risk of tissue freezing.
Known second generation mid-boiling refrigerants, including 124 and 142B, have much lower boiling points than the corresponding mid-boiling CFC components, e.g. 12.2 F. and 14.4 F. respectively and therefore pose a substantial risk of tissue freezing when substantial quantities of refrigerant liquid (at about atmospheric pressure) vaporize in proximity to the skin. Conventional CFC-based systems need not carefully control the flow of refrigerant, because the major penalty of too high a flow rate is the premature exhaustion of the CFC supply and a high flow rate of gas (and/or liquid in extreme cases) exhausted from the system.
The following patents relate to known refrigerant systems: Lodes, U.S. Pat. No. 2,529,092; Benning, U.S. Pat. No. 2,641,579; Ashkenaz, U.S. Pat. No. 2,987,438; Munro, U.S. Pat. No. 3,733,273; Borchardt, U.S. Pat. No. 3,812,040; Hutchinson, U.S. Pat. No. 3,940,342; Murphy, U.S. Pat. No. 4,055,054; Orfeo, U.S. Pat. No. 4,533,536; Nikolsky, U.S. Pat. No. 4,495,776; Ermack, U.S. Pat. No. 4,510,064; and Nikolsky, U.S. Pat. No. 4,603,002.
Brown, U.S. Pat. No. 2,694,395 relates to a pneumatic pressure garment for application of therapeutic pressure. Gottfried, U.S. Pat. No. 3,153,413 relates to a pressurized bandage with splint functions. Towle, et al., U.S. Pat. No. 3,171,410 relates to a pneumatic wound dressing. Gardner, U.S. Pat. No. 3,186,404 relates to a pressure device for therapeutic treatment of body extremities. Romano, U.S. Pat. No. 4,135,503 relates to an orthopedic device having a pressurized bladder for spinal treatment. Curlee, U.S. Pat. No. 4,622,957 relates to a therapeutic corset for applying pressure to a portion of the back. Cronin, U.S. Pat. No. 4,706,658 relates to a gloved splint, providing a shock absorbing treatment and possible heat removal from the hand.
Robbins et al., U.S. Pat. No. 4,175,297 relates to an inflatable pillow support having automated cycling inflation and deflation of various portions thereof.
Artemenko et al., U.S. Pat. No. 3,683,902 relates to a medical splint apparatus, having an inflatable splint body and a circulated cooling agent, cooled by solid carbonic acid CO.sub.2. Davis et al., U.S. Pat. No. 3,548,819 relates to a pressurized splint adapted to apply a thermal treatment to a human extremity. Nicholson, U.S. Pat. No. 3,561,435 relates to an inflatable splint having a coolant chamber to apply pressure and cool to a human extremity. Berndt et al., U.S. Pat. No. 3,628,537 relates to a self-retaining cold wrap which treats an injury with cold and pressure. Baron, U.S. Pat. Nos. 4,300,542 and 4,393,867 relate to a self-inflating compression device for use as a splint.
Golden, U.S. Pat. No. 4,108,146 relates to a cooling thermal pack with circulating fluid which conforms to body surfaces to apply a cooling treatment. Moore et al., U.S. Pat. No. 4,114,620 and Gammons et al., U.S. Pat. No. 4,149,541 relate to treatment pads with circulating fluid for providing a hot or cold treatment to a patient. Brannigan et al., U.S. Pat. No. 4,575,097 relates to a thermally capacitive compress for applying hot or cold treatments to the body.
Arkans, U.S. Pat. No. 4,331,133 relates to a pressure measurement apparatus for measuring the pressure applied by a pressure cuff to a human extremity.
Kiser et al., U.S. Pat. No. 4,502,470 relates to a device for assisting in pumping tissue fluids from a foot and ankle up the leg.
Stark, U.S. Pat. No. 3,000,190 relates to an apparatus providing body refrigeration, for use in high ambient temperature environments by workers.
FR 2,133,680 relates to a system for cooling objects, including beverage cans, using fluorocarbons, e.g. Freon.
Nelson, U.S. Pat. No. 2,051,100, Burkhardt, U.S. Pat. No. 2,463,516 and Richards, U.S. Pat. No. 4,103,704 relate to pressure relief valves.
Ninomiya et al., U.S. Pat. No. 4,286,622 relates to a check valve assembly.
Martin et al., U.S. Pat. No. 2,550,840, Both et al., U.S. Pat. No. 2,757,964, Galeazzi et al., U.S. pat. No. 2,835,534, Mura, U.S. Pat. No. 3,314,587, White, U.S. Pat. No. 3,976,110 and Turner, U.S. Pat. No. 4,281,775 relate to pressurized container dispensing valves and systems containing same. Frost, U.S. Pat. No. 3,273,610 relates to a pressurized container valve and detachable dispensing attachment device.
Known aerosol-type cans have a stem which protrudes upwardly, and which is depressed to release the contents of the can. The nozzle is generally secured to the stem by friction. A cap is generally provided to prevent inadvertent release of the contents of the can. Known refrigerant-supply cans are generally sealed and release their contents only after a metal diaphragm is punctured. Thus, Vos, U.S. Pat. No. 3,756,472 relates to a system for use with a pressurized canister to produce a desired stream characteristic during ejection of the pressurfzed contents. This system may be mounted atop an aerosol container.
Portability, a desired characteristic, requires a system which has good long term storage capability, ease of replacement of any expendable components, and light weight self-contained design, without need for an external power source and relatively safe design.